The present invention relates to hand held battery powered electronic and electrical devices, and more particularly, to flashlights designed to prevent explosions due to outgassing of flammable gases from batteries.
In order to make alkaline batteries less hazardous to the environment, Mercury is no longer used as a constituent thereof. However, this leads to increased outgassing of hydrogen gas, especially when multiple batteries are inserted into a flashlight or other portable or electrical device without the proper positive-to-negative terminal orientation required, i.e. correct polarization.
Many flashlights have substantially watertight, and therefore substantially gas impervious battery housings so that they will still function if submerged in water. There have been instances where such flashlights have exploded due to the build-up of hydrogen gas therein. Such explosions not only risk personal injury, but can also be catastrophic where a fireman is inspecting a building with a propane leak, or a worker is inspecting a grain silo, for example. An entire building or silo can explode, killing individuals and inflicting staggering property losses. Apart from the hazard of explosion, incorrect battery polarization can cause alkaline batteries to leak potassium hydroxide. This chemical can seriously corrode terminals and other contacts within a flashlight, rendering it non-functional.
Attempts have been made in the past to address the danger of hydrogen gas emission inside substantially airtight flashlights. Pellets have been installed into the lamp module of a flashlight as disclosed in U.S. Pat. No. 5,404,281 of Parker to absorb or otherwise render harmless any hydrogen gas expelled by the batteries. Such pellets may include Aluminum Oxide and Platinum which acts as a catalyst so that water vapor is produced. The problem with such pellets is that they degrade over time so their ability to neutralize the hydrogen gas emitted by the batteries may be insufficient. Another approach to dealing with the hydrogen gas emitted by flashlight batteries is disclosed in U.S. Pat. No. 5,349,507 of Parker wherein a pressure release valve is incorporated into the battery housing to vent hydrogen gas. The construction of the valve includes a coil spring and a sealing plate and it requires a minimum pressure of at least two and one-half pounds per square inch relative to the ambient air before the hydrogen gas will vent. Clearly accumulated hydrogen gas within the battery housing having a pressure below this amount could still ignite based on the oxygen within the housing, causing an explosion.